Florida beggarweed (Desmodium tortuosum (SW.)DC) is a major weed problem in many fields in the Southeastern United States where peanuts and soybeans are grown. It is ranked as the most troublesome weed in peanuts in the three largest peanut producing states, and its spread is causing increasing concern to farmers throughout the Southeast. This weed occurs primarily in field crops, but is found also in fallowed areas and along roadsides and waste areas. Florida beggarweed is an annual herbaceous legume native to Florida and the Gulf States, extending to the subtropics and tropics of the Western Hemisphere. Although it is currently considered one of the most damaging weeds, particularly in leguminous crops, Florida beggarweed was a popular forage crop prior to 1950. As a forage crop, heavy seeding on land of moderate to high fertility was recommended so that when plants matured 70-80 days later, the crop could be expected to yield 4 to 6 tons of dry matter and return to the soil up to 5000 seeds per plant. As a result, Florida beggarweed, no longer considered an acceptable forage crop, plagues farmers throughout the Southeast on soils that are most suitable for peanuts and soybeans. The damage caused by Florida beggarweed is primarily a result of competition with the field crop for light, water, and nutrients. In addition, this weed, which may reach 10 feet at maturity, overtops the crop canopy and interferes with pesticidal spray programs. Particularly serious is the decreased coverage of biweekly foliar fungicide applications in peanuts caused by infestations of Florida beggarweed. In peanut production, where the crop must be inverted at the end of the season, Florida beggarweed interferes with the digging, turning and curing processes, and thereby causes further reductions in crop yield and quality.
Florida beggarweed harbors several pests of field crops. It is a common late-season food source for Heliothis virescens larvae, a pest of numerous crops. This weed is also a host of northern rootknot, lesion and sting nematodes that severely damage many crops. Recent evidence indicates that Florida beggarweed is a host of peanut mottle virus and peanut stripe virus.
Florida beggarweed is a leguminous weed that is not controlled by herbicide programs recommended for use in peanuts and soybeans. Development of chemical control for Florida beggarweed is complicated by its close botanical relationship to peanuts, soybeans, and other leguminous crops. This puts unusually stringent selectivity requirements on development of herbicides.
Chemical weed control programs are seriously inadequate for control of this weed. Florida beggarweed is resistant to many herbicides used in peanuts and soybeans. Frequently the weed germinates below the treated zone and avoids herbicide injury. Although many herbicides have been developed and tested in the last three decades, farmers still rely heavily on dinoseb, a herbicide developed in the 1950's. Dinoseb is a contact herbicide that causes injury to peanuts and soybeans; farmers tolerate this injury out of the necessity to control Florida beggarweed. Alternative approaches include MSMA (monosodium methanearsonate) paraquat, toxaphene and triazine herbicides, but these chemicals are not registered for use on these crops for reasons of toxicology and/or crop safety. Other inadequacies of chemical controls include lack of residual control, injury to nontarget organisms, undesirable residues in harvested products and carryover in subsequent crops.
The use of bioherbicides is becoming an increasingly important alternative to chemical herbicides for a variety of reasons, some of which are similar to those experienced in the chemical control of Florida beggarweed, as disclosed above. This importance is accompanied by several patents which have issued for bioherbicides and their use. Some of these patents, by way of illustration, are as follows: U.S. Pat. No. 3,849,104 (control of northern jointvetch with Colletotrichum gloeosporioides Penz. aeschynomene); U.S. Pat. No. 3,999,973 (control of prickly sida [teaweed] and other weeds with Colletotrichum malvarum); U.S. Pat. No. 4,162,912 (control of milkweed vine with Araujia mosaic virus); U.S. Pat. No. 4,263,036 (control of Hydrilla verticillata with Fusarium roseum Culmorum); U.S. Pat. No. 4,390,360 (control of sicklepod, showy crotalaria, and coffee senna with Alternaria cassiae); and U.S. Pat. No. 4,419,120 (control of prickly sida, velvetleaf, and spurred anoda with fungal pathogens.